The present invention relates to an improved apparatus for the restoration of paintings, documents and the like. More particularly, this invention pertains to method and apparatus of restoration, preferably of paintings, to preserve the original texture of the painting. In accordance with the invention, an improved technique is disclosed for lining a painting without causing any damage to the texture of the painting.
The visual impact of a specific painting is derived from a unique combination of color, composition, size and shape, and texture. Altering any one of these properties, naturally, can considerably modify or even destroy the artist's intention. Usually the size and shape of a finished painting remain the same, as does its composition. In restoration, one of the key steps that can effect the aesthetic characteristic of the painting is the method of lining that is used to provide support for the work of art. Improper techniques can cause physical damage to the paint film as well as a change in the textural quality of the painting.
Most paintings that are now being restored are paintings that were formed on canvas. Canvas is not a rigid or solid material. Rather, it consists of fine filaments of fiber twisted into strands which then are woven into a somewhat loose mesh. The strands are not uniform in dimension, being thicker or thinner along their length, and having small gathers of fiber at intervals called slubs. When woven, several strands of the warp or weft may be of different diameter than adjacent ones, and along them are occasional lumpy slubs.
The entire paint film may consist of one or more layers: a thin glue sizing, a coat of primer and the paint applied by the artist. None of this penetrates the canvas, but rests mainly upon the surface of the fibers. In other words, a painting on canvas is a pigment layer or a composite paint film that is weakly bonded to the canvas underneath. Although a canvas is a durable material it it susceptible to deterioration over time and also to damage from physical accidents.
To protect paintings for about the past 300 years, linings have been bonded to the canvas using various adhesive systems. Originally, linings were attached using an animal or vegetable-base aqueous glue. This required the use of weights, presses or similar devices to maintain the necessary contact while the glue set. Although this glued lining helped to delay structural damage of the canvas, it often had negative effects on the paint layers. That is, when the work of art had been painted on a canvas prepared with an aqueous glue sizing, the moisture released during the lining process reacted with the sizing and caused the sizing (and with it, the painting) to detach and flake off. In addition, the mechanical pressure necessary to insure adhesion marred the surface texture -- impastos were pressed into the paintings, and delicate passages flattened.
Toward the end of the 19th century, the aqueous glue was replaced by a mixture of wax with gum tactifiers. This mixture, being thermoplastic, needed heat for the application and joining of lining and painting. The destructive effect of moisture was eliminated, but ironing, the required method with wax, presented its own problems. That is, how could a flat and even contact be maintained as work progressed over the surface of the painting while the wax was cooling and setting.
This problem was overcome by the development of a hot table -- a table with a heated top which permitted weighted boards to hold the work flat until it was completely cold. Soon thereafter, in the 1950's a vacuum pressure was used as the means of force against the painting surface. This vacuum pressure was used in the form of a vacuum hot table. This method of covering the painting with a large plastic membrane and pumping out the air beneath was originally conceived as a procedure that would produce a soft and innocuous pressure to keep the painting and new lining flat and in uniform contact throughout the lining process. However, there were indications that paintings lined in this manner displayed disfiguring textural impressions from the subsurface irregularities in the lining fabric. This prior art technique typically employed treatment in a single operation on a hot table combining heat in the range of 150.degree. F.-165.degree. F. along with vacuum pressures ranging from 5"-20" of mercury.
There has been a clear indication through tests and other investigations that alterations to the artistic texture can reach maximum proportions under vacuum pressures even as low as 5" of mercury in some instances. While all paintings are not equally sensitive to lining pressures, either vacuum or mechanical, there is no other way than by empirical means to determine whether or not textural damages will occur during lining. Furthermore, considering the potential danger that vacuum poses to delicate and susceptible paintings, the general design of the vacuum hot table is not adequate for such delicate operations. For one thing, the commercially available vacuum hot tables are equipped with vacuum pumps far in excess of the requirements. Therefore, an excessively high vacuum could be attained in a fraction of a second if the operation is not conducted carefully. These tables are provided with vacuum outlet holes in the corners; the vacuum being achieved by covering the lining work with an air-tight membrane. The removal of air may be made more even with the use of porous tapes or strips. However, it has been found that the vacuum levels are indeed non-uniform over the painting surface especially with large paintings. Also, the pressure is usually measured at the pump which is indeed inaccurate as it is the pressure at the surface of the painting that should be measured.
The manner in which vacuum membranes are employed to seal out air and achieve pressure gives rise to further problems which come about as temperatures increase during the heating cycle of the lining process. As the membrane warms it becomes more flexible and clings more closely to the table top providing a more effective air seal. Vacuum pressure balance previously set can then begin to rise, often without the knowledge of the operator because such pressure increases do not always show immediately on the system gage. The dangers inherent in this are obvious, and the vacuum hot table systems frequently lack arrangements to prevent unwanted pressure increases.
All of these factors, excessively powerful pumps, inefficient air flow, unequal vacuum pressures, absence of positive pressure control devices, and leaky air seals around the membrane edges which can open and close as heat and vacuum vary and cause fluctuations in vacuum pressure do not register on the system gage located near the pump -- add up to a great inability to adequately control operating conditions. Therefore, there are definite textural changes that take place in the texture of the painting with the use of the present vacuum hot table systems.
Accordingly, it is an object of the present invention to provide an improved means and method for the restoration of paintings, documents and the like.
Another object of the present invention is to provide an improved cold adhesion system for the lining of paintings, preferably for use with paintings requiring only the attachment of a lining.
Still another object of the present invention is to provide an improved means and method for the restoration of paintings and in particular for the restoration of the lining of the paintings without causing any damage to the painting and without altering the original texture of the painting.
A further object of the present invention is to provide an improved means and method of restoring paintings to their original planar composition without the requirement for significant forces applied perpendicular to the surface of the painting.
Still another object of the present invention is to provide an improved apparatus useful in the restoration of paintings and which employs an electrostatic hold technique rather than the more troublesome prior technique of vacuum pressure.